Poppo I of Blankenburg (ca. 1095–1161 or 1164) probably came from the House of Reginbodonen and was Count of Regenstein-Blankenburg in the Harz in central Germany.
His uncle was the Bishop of Halberstadt, Reinhard of Blankenburg, who probably paved the first steps for him.
As the vassal of Duke Lothair of Supplinburg he exercised count's rights in the Harzgau and was later recorded as a vassal of Henry the Lion. From 1128 he was given the title of comes. His county, which had probably been created by his in-law, Lothair of Supplinburg, was in the eastern Harzgau between the rivers Ilse and Bode. (Lothair was also an in-law of Burchard I of Loccum).
He married Richenza of Boyneburg, the daughter of Count Siegfried III of Boyneburg.
In 1163 as the brother-in-law of the late count, Siegfried IV of Boyneburg, who had died in 1144, he brought certain claims agains Northeim Abbey, mediated by his wife, Richenza, before Henry the Lion, who had to uphold them.